Liquid developing system



y 1968 F. HUNSTIGER 3,392,708

LIQUID DEVELOPING SYSTEM Filed Sept. 1, 1966 TONER CCNCENTRATE THINNERSUPPLY 30 FIG -2 INVENTOR FRANCIS HUNSTIGER ATTORNEYS United StatesPatent Ofiiice 3,392,708 Patented July 16, 1968 3,392,708 LIQUIDDEVELOPING SYSTEM Francis Hunstiger, Parma Heights, Ohio, assignor toHarris-Intertype Corporation, Cleveland, Ohio, a corporation of DelawareFiled Sept. 1, 1966, Ser. No. 576,592 4 Claims. (Cl. 118-637) ABSTRACTOF THE DISCLOSURE A roll-type electrostatic liquid developer with animpeller shaft mounted transversely of the output side of the tank,impellers on the shaft for circulating the developer liquid peripherallyof the tank, and a supply of thinner and a separate supply of toner foradmittance into a mixing zone including the impeller for peripheralcirculation to the inlet side of the developer.

The invention relates to improvements in systems for developingelectrostatic and electrophotographic images, and more particularly to adeveloper tank and developer mixing and circulating structure for suchsystems.

In liquid developing systems of the type indicated, a web bearing alatent electrophotographi-c image is brought into contact with adeveloper liquid, and a visible image is formed thereon by thedeposition of toner particles from the developer liquid onto a surfaceof the sheet material. A system of this general type is shown anddescribed in the copending application of Hunstiger et al., Ser. No.372,503 filed June 4, 1964, now Patent No. 3,307,458, and assigned tothe same assignee as this invention. In such systems, it is desired tomaintain a relatively constant level of developer within the tank.However, it is necessary constantly to replenish the developer in thetank as the various sheets or lengths of material pass through thedeveloper tank or as a continuous web of such material passes through,whichever may be the case.

The developer liquid may be as described in the copending applicationsof Fauser et al., Ser. No. 762,756, filed Sept. 23, 1958, now Patent No.3,311,490, and Ser. No. 420,449, filed Dec. 22, 1964, now abandoned, allassigned to the same assignee as this invention. Such developers includeparticles of toner which are in suspension in an insulating thinner.Toner particles may be formed of controlled agglomerations of pigmentsand resins, known as association complexes, and may be made up of apigment and one or more bonding resins, held in suspension in a suitablehydrocarbon thinner liquid, as described in application Ser. No.420,449.

Not only is it desirable to maintain a constant level of developer inthe developer tank, but it is also highly desirable to maintain aconstant concentration of the toner complexes with respect to thethinner. However, the toner and thinner are each being depleted somewhatindependently of each other during the operation of the system. It istherefore desirable to add toner from a supply of toner concentrate tothe tank independently of the supply of thinner, and each according todemand, in order to maintain desired concentration of toner-to-thinnerin the developer liquid, to maintain constant quality of reproduction ofthe latent images. It is also desirable to maintain such concentrationuniformly across the width of the incoming sheet material to avoidstreaking and thinly developed areas on the material.

The developer, as described above, is susceptible to degradation due toexcessive mechanical shear or agitation. This is believed due to thefact that the complexes of resin and toner are broken, wherein charge islost, by excessive mechanical working or friction, reducing the totaleffectiveness of the developer liquid. It is accordingly important toavoid such shear and stresses which would result in degradation of thedeveloper.

These desired objects are met by the apparatus of this invention whichprovides for the addition of thinner from a thinner supply andindependently the addition of toner from a supply of toner concentrate.These separate parts are supplied in accordance with demand and aredirected to a mixing zone in the apparatus which is remote from theinlet side of the developer tank into which the sheet material is beingfed.

The system also includes apparatus for effecting a circular orperipheral flow of developer liquid through the mixing zone at a ratewhich is sufficient to mix the toner concentrate and thinner but whichdoes not cause degradation of the toner. This mixing apparatuspreferably forms a peripheral circulation around the tank whichconstantly supplies developer liquid at a desired and uniformconcentration to the region of the tank at which the sheet materialenters.

Preferably, the sheet material is guided and supported for movementthrough the tank on a drum roll. Due to friction between the sheetmaterial and the liquid developer, the movement of the sheet materialwith the rolls acts as a pump and causes circulation of developer fromthe inlet to an outlet side of the tank. The tank construction of thisinvention provides for a secondary circulation of the developer in aperipheral manner around the tank by flow in spaces between the ends ofthe ends of the developer roll. Preferably, this circulation issulficient to maintain makeup developer at the inlet side, and thereforeexceeds the rate of liquid developer withdrawn due to the pumping actionby reason of the sheet material moving through the tank.

It is accordingly a primary object of this invention to provide a liquiddeveloper system, as outlined above, in which a liquid developer tank isprovided with a mixing zone remote from the inlet side of the tank,together with apparatus for adding toner concentrate and thinnersubstantially at said mixing zone.

A further object of this invention is the provision of developingapparatus, as outlined above, in which a toner concentrate and a thinnerare each added through independently controlled supply conduits to adeveloper tank.

A further object of this invention is the provision of a developingsystem, as outlined above, in which mechanical mixers and pumpingelements are provided in a mixing zone to provide a peripheral or asecondary circulation of developer fluid for mixing a toner concentratewith a thinner and for maintaining a uniform concentration of developerat the inlet side of the tank.

These and other objects and advantages of the present invention will beapparent from the following description, the accompanying drawing andthe appended claims.

In the drawing.

FIG. 1 is a perspective and somewhat diagrammatic view of a developersystem constructed according to this invention; and

FIG. 2 is a perspective view of one of the impellers used with thisinvention.

Referring to the drawing, which illustrates a preferred embodiment ofthe invention, an open-top liquid developer tank is shown at 10 in FIG.1 as including a partially semi-circular bottom 11 enclosed withopposite end walls 12 and 13.

The open top of the tank 10 receives a drum roll 15 therein so that thesurface of the drum roll forms a relatively close running fit with thesemi-circular bottom 11. The drum roll 15 has a diameter which isgreater than the depth of the tank 10, so that an upper portion of thedrum roll extends above the open side of the tank 10,

3 and has a length less than the width of the tank to define spaces 16and 17 at each end thereof with the respective end walls 12 and 13.

The drum roll provides the means for supporting movement of sheetmaterial 18 through the developer tank 10 from an inlet side 19 of thetank generally to an outlet side 20 in a direction of movement indicatedby the arrows 21. The sheet material 18 may consist either of individualsheets or a continuous web of indeterminate length, upon which anelectrophotographic image is formed.

As shown in FIG. 1, the inside surface of the sheet material 18 engagesthe drum roll 15 in intimate contact therewith prior to entering thetank 10, so that the inside surface of the sheet material 18 is incontact with the outside surface of the drum roll 15 at all times whichis submerged within the tank and accordingly remains dry, while theoutside surface becomes fully immersed within the liquid developerwithin the tank. The latent image on the outside surface of the sheetmaterial 18 is developed as it passes through the developer 25 in themanner described in the above-identified applications.

As the material 18 leaves the tank 10 at the outlet side 20, it issubjected to the developer removing action of a nip formed between asqueegee roll 26 and the drum 15. The squeegee roll 26 may be partiallysubmerged within the liquid developer 25, or may be positioned above thelevel of the developer, as shown in FIG. 1, and removes the excessdeveloper fluid from the image side of the sheet material 18 as itleaves the tank.

Since the outer surface of the sheet material 18 is wetted by thedeveloper, at certain amount of the thinner is removed from thedeveloper 25. This is constantly made up to maintain a liquid level inthe tank from a thinner supply 30-by a pump 31 connected to a floatchamber 32 mounted on the end wall 12. The chamber 32 opens into thetank 10 and contains a float and needle valve assembly 33 which isresponsive to the level of the liquid 25 and maintains this levelconstant by admitting thinner from the thinner supply 30 into theadjacent end space 16 formed between the end of the drum 15 and theadjacent wall 12.

Toner is removed from the developer 25 by deposition onto the sheetmaterial in accordance with the density of the image. Means forseparately adding toner includes a supply 40 of toner connected by atube 41 to an electrically solenoid-operated valve 42 which iscontrolled by a solenoid 43. The valve 42 is positioned to dischargetoner concentrate into one end of a mixing zone 45 formed on the tankadjacent the tank outlet side 20 and remote from the inlet side 19. Forthis purpose, the tank 10 is formed with a forwardly extending bottomportion 48 formed as a continuation of the bottom 11 but having a depthwhich is substantially less than the overall depth of the tank at theroll 15. The bottom portion 48 is terminated with an upwardly formedfront wall 49 and forms with the previously described end walls 12 and13 a tank extension positioned forwardly and adjacent to the outlet side20 and in generally underlying relation to the squeegee roll 26,defining the zone 45.

The mixing zone 45 is accordingly in communication with the liquid 25within the tank and may be considered as being formed as an integralextension of the tank, and extends the full width of the tank, toreceive liquid therein from the peripheral end spaces 16 and 17 as wellas from the circulation due to the movement of the material 18 from theinlet side 19 to the outlet side 20. The toner concentrate from the tank40 is admitted substantially at one end of the mixing zone 45,preferably at the same side of the tank 10 at which the thinner is addedby the float chamber 32.

The mixing zone 45 includes mixing and impeller means for mixing thetoner concentrate and thinner with the liquid 25 and for forming aperipheral or circular endwise circulation of the liquid, designated bythe arrows 1 4 v 50. This impeller means includes a plurality ofdisk-like impellers 52 (FIG. 2) mounted on a common shaft 53 extendingfor rotation through the zone 45 between the end walls 12 and 13. Theshaft 53 is positioned such that all of the impellers 52 are submergedbeneath the level of the liquid 25.

A relatively slow-tuming drive motor 55 is connected to rotate the shaft53 at a rate which is suflicient to cause the impellers 52 to mix theincoming thinner and toner concentrate and to direct the same in thegeneral direction of the arrows 50 peripherally by flow through the endspaces 16 and 17 formed at the opposite ends of the drum, and across theinlet side 19 of the tank 10. The rate of circulation is not critical,but preferably exceeds that caused by the pumping action of the roll 15and material 18, as indicated by the broken arrows 58, so that a freshsupply of developer is at all times supplied across the width of the web18 in the inlet side 19.

As shown in FIG. 2, the impeller 52 may include a hub on which a slotteddisk 63 of sheet material is formed with partially radially extendingslots 65 defining four vanes 68. The vanes 68 are suitably angulated toform an impeller of high lift pitch. Good results have been obtainedwith impellers of approximately 1% inches in diameter at 5-6 inchspacing along the shaft 53, operating at 300 r.p.m., but these sizes,spacing and speed are not considered critical as lOng as the volumetricdisplacement of the combined impellers is sufiicient to provide theperipheral circulation in excess of the requirements at the inlet side19 of the tank, with sufficient motion to mix the added tonerconcentrate with the added insulating thinner and liquid 25 withoutdegradation of the toner agglomerations.

The supply of toner is controlled by the periodic operation of thesolenoid 43. This may be controlled, in turn, in accordance with a timedcycle, but is preferably controlled in accordance with the amount ofprinting on the material 18 moving through the system. For this purpose,the drum roll 15, or a proceeding roll in the system, may be suppliedwith a suitable timing cam which operates a timer whose setting isadjusted proportional to the printed area which operates solenoid 43intermittently. In this manner, the amount of toner is added as afunction of the printed area on the sheet material 18.

It will therefore be seen that this invention provides a developersystem in which the insulating thinner and the toner concentrate areseparately added and are mixed in a zone remote from the inlet side ofthe tank and in which a secondary or peripheral circulation ismaintained to supply a recharged developer mixture at the input or inletside of the drum, providing uniform developing across the width of thedrum and a uniform quality of the developer liquid.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. In an electrostatic liquid developing system, the improvement indeveloper construction comprising a liquid developer tank, means forguiding sheet material having an electrostatic image thereon into aninlet side of said tank and out of an outlet side thereof causing thedevelopment of said electrostatic image by deposition of toner materialfrom the developer liquid in said tank and causing a first circulationof developer fluid in said tank generally from said inlet to said outletsides by reason of the movement of said sheet material therethrough,means for adding developer thinner to said tank maintaining apredetermined level of developer thereon, means in said tank defining adeveloper mixing zone remote from said inlet side, means for addingtoner concentrate into said tank substantially at said mixing zone, andimpeller means in said zone for combining said thinner and said tonerconcentrate and effecting a secondary circulation of said liquidperipherally about said sheet guiding means for supplying make updeveloper at said inlet side maintaining a balanced concentration ofsaid developer, said impeller means being eflective to cause saidsecondary circulation at a rate which exceeds that of said firstcirculation.

2. The developer system of claim 1 in which said sheet material guidingmeans comprises a drum partially submerged in said tank for guiding saidsheet material from said inlet side to said outlet side, a squeegee rollpositioned to apply pressure against said drum positioned generallyabove said outlet side for removing excess developer from said sheetmaterial, means in said tank at the opposite ends of said drum definingopen spaces providing for said peripheral circulation of said developerfluid past the ends of said drum.

3. The system of claim 2 in which said mixing zone is positionedadjacent said outlet side in said tank, and extending transverselysubstantially the width of said drum, said impeller means comprising aplurality of impellers positioned in said mixing zone for effecting saidperipheral circulation, and motor driven means connected to rotate saidimpellers at a rate suflicient to supply makeup developer liquid throughsaid peri heral circulation to the said inlet side of said tank whilepreventing excessive shear and agitation which would cause degradationof said developer.

4. In an electrostatic liquid developing system, the improvement indeveloper construction comprising a liquid developer tank having endwalls and a semi-circular bottom, 9. roll partially received in saidtank for guiding sheet material having an electrostatic image thereoninto an inlet side of said tank and out of an outlet side thereofcausing the development of said electrostatic image by deposition oftoner material from the developer liquid in said tank and effecting acirculation of developer fluid in said tank generally from said inlet tosaid outlet sides by reason of the movement of said sheet materialtherethrough, means between said tank end walls and the ends of saidroll defining passageways for the flow of developer liquid therethrough,means in said tank defining a developer mixing zone adjacent the saidoutlet side of said tank opening into each of said passageways, floatmeans for adding developer thinner to said tank for mixing in said zone,means for adding toner concentrate into said tank for mixing at saidmixing zone, and impeller means in said zone for combining said thinnerand said toner concentrate and effecting a secondary circulation of saidliquid through said passageways for supplying make up developer at saidinlet side maintain a balanced concentration of said developer.

References Cited UNITED STATES PATENTS 3,227,549 1/1966 Ullrich et al96-1 3,242,902 3/1966 Ulary 118-637 3,284,224 11/1966 Lehmann 117-17.53,299,787 1/1967 Kolb et al. 118637 XR FOREIGN PATENTS 938,349 10/1963Great Britain.

CHARLES A. WILLMUTH, Primary Examiner. PETER FELDMAN, AssistantExaminer.

